Vehicle steering system of the fluid power type and spring centered, spring modulated control cylinder therefor

ABSTRACT

A vehicle steering system having a pair of fluid power cylinders for simultaneously actuating each wheel of a pair of steerable wheels, and also having a control cylinder for one of the power cylinders of each pair to cause said power cylinders to be actuated to different extents, consequently producing angular rotation of said steerable wheels in like directions, but in different amounts. An improved spring centered and spring modulated control cylinder which is extended at a different rate than it is contracted.

United States Patent 1151 3,696,88 1 Gordon [4 Oct. 10, 1972 [54]VEHICLE STEERING SYSTEM OF THE 3,148,744 9/ 1964 De Stasi ..180/79.2 RFLUID POWER TYPE AND SPRING 3,532,178 10/ 1970 Lindbom 1 80/792 C ENTESPRING MODULATED 3,602,326 8/1971 Garrison ..l80/79.2 R CONTR CYLINDERTHEREFOR R ,981 3/1966 Baudhuin l 79.2 R

Inventor: Richard 0. Gordon, Belgium, Wis.

Harnischfeger Corporation, Milwaukee, Wis.

Filed: June 16, 1971 Appl. No.: 153,492

Assignee:

us. c1. ..1s0/79.2 R,'60/52 s, 91/189, /792 c 1111. c1. ..B62d 5/08Field of Search... 1 80/792 RC; 60/52 s; 91/189, 91/413 References CitedUNITED STATES PATENTS Kupiec 180/792 R X Primary Examiner-Benjamin HershAssistant Examiner-Leslie J. Paperner Attorney-James E. Nilles [57]ABSTRACT A vehicle steering system having a pair of fluid powercylinders for simultaneously actuating each wheel of a pair of steerablewheels, and also having a control cylinder for one of the powercylinders of each pair to cause said power cylinders to be actuated todifferent extents, consequently producing angular rotation of saidsteerable wheels in like directions, but in different amounts.

An improved spring centered and spring modulated control cylinder whichis extended at a different rate than it is contracted.

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[m /up 4. 60100 VEHICLE STEERING SYSTEM OF THE FLUID POWER TYPE ANDSPRING CENTERED, SPRING MODULATED CONTROL CYLINDER THEREFOR BACKGROUNDOF THE INVENTION The present invention pertains to vehicle steeringapparatus of the fluid power type.

An example of theprior art of this general type of steering apparatus isshown in the US. Pat. No. 3,148,744, which issued Sept. 15, 1964 toDeStasi, entitled, Vehicle Steering System and Including CompensatingSteering Linkage. The apparatus shown in that patent utilized a rathercomplicated linkage arrangement as the means for simultaneouslyactuating servo valves to different extents, to thereby cause theirassociated power cylinders to be actuated in different amounts, tothereby produce angular rotation of the steerable wheels. That prior artapparatus, as does the present apparatus, insures that the two wheelsbeing steered are turned in different angular amounts to thereby preventscuffing or skidding of the tires. That is to say, the apparatus causesthe wheel at the inside of the turn to be angularly moved to a greaterextent than the outer wheel, thereby providing that the center lines ofall of the wheel axles meet at a common point, and which common pointmay shift with changes in the steering angle.

Other conventional methods of steering a pair of wheels simultaneouslyhave included the use of a mechanical tie bar or drag link assemblyorientated in the correct position to compensate for the difference ofangular movement of the wheels, thereby causing the vehicle to effect aturn without slipping or scuffing of the tires. These prior art deviceshowever, are not usable with certain types of vehicles, such as withgantry cranes or the like wherein the space between the wheels must bekept clear for the carrying of the article being transported.

SUMMARY OF THE INVENTION The present invention provides a steeringsystem for a vehicle of the type having at least two steerable wheels,and which steering system utilizes a pair of fluid power cylinders foreach of the two wheels being steered. The system includes a springcentered control cylinder having a first spring for returning thecylinder to neutral and also has a modulating spring so that the controlcylinder does not retract at the same rate at which it extends. Such acontrol cylinder is provided for actuating the fluid valve of one of thepower cylinders of each of the steering wheels. Consequently, when thevehicle is turned in one direction, that control cylinder located at theinside of the turn extends and is not influenced by the said modulatingspring, while the control cylinder located in connection with the wheelat the outside of the turn, is contracted and due to its modulatingspring is not contracted at the same rate at which the opposite controlcylinder is extended. Thus, the outer wheel is turned to a lesser degreethan the inner wheel.

The resulting control system is a fully hydraulic system which utilizesno compensating connecting linkages between the servo valve and theoperator control. The present steering apparatus furthermore utilizes notie bar and drag link assembly, push-pull cables or other extracomponents as are found in other prior art types of steering systems.

Another aspect of the present invention provides an improved controlcylinder which is spring centered and which also has a modulating springfor providing that the control cylinder contracts at a different, slowerrate than it extends. Thereby the control cylinders act to admit fluidto their respective power cylinders at different rates, depending onwhether they are being contracted or extended, as in a situation wherethey are used for steering a pair of wheels.

These and other objects and advantages of the present invention willappear hereinafter as this disclosure progresses, reference being had tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of agantry crane embodying the present invention;

FIG. 2 is a front elevational view of the gantry crane shown in FIG. 1;

FIG. 3 is an enlarged, fragmentary view of a portion of the steeringmechanism as shown in FIG. 1, certain parts being shown as broken awayor in section for clarity;

FIG. 3a is a view taken generally along the line 3a- 3a in FIG. 3;

FIG. 4 is a bottom view of the mechanism shown in FIG. 3, certain partsbeing shown as broken away or in section for the sake of clarity;

FIG. 5 is a perspective view of the device shown in FIG. 3, the viewbeing taken generally from beneath the device;

FIG. 6 is a cross sectional view of the control cylinder shown in theother figures, certain parts shown as broken away;

FIG. 7 is a schematic view depicting the control system of the presentinvention as applied to two steerable wheels of the gantry crane, asshown in FIGS. 1 and 2; and

FIG. 8 is a further enlarged view showing the control cylinder and thetwo power cylinders for one wheel assembly.

DESCRIPTION MENT The invention has been shown and described as appliedto a mobile gantry crane C, although other types of cranes such asstraddle cranes or the like are particularly suited for the presentinvention. If a more detailed description of the particular gantry craneC shown is deemed to be either necessary or desirable, reference may behad to the US Pat. No. 3,247,975, which issued Apr. 26, 1966 to Holt etal. and entitled Mobile Gantry Crane having a Resiliently SupportedBridge. It is believed sufficient to say for purposes of the presentdisclosure that the crane shown includes an upper, generally horizontal,transverse girder 1 having a pair of downwardly diverging legs 2 and 3at one end and another pair of downwardly converging legs 4 and 5 at theother end of the girder. A longitudinally extending sill 7 connects thelower ends of the legs 2 and 3, while another parallel sill 8 connectsthe lower ends of legs 4 and 5.

When viewed in FIG. 2, it will be noticed that the entire expansebetween the pair of legs 2, 3 and the pairs of legs 4, 5 is open andunobstructed so that a load (not OF A PREFERRED EMBODI- shown) may besuspended from the transverse girder 1 and between the opposite pairs oflegs.

At each end of each sill is a vertical bearing which journals itsrespective steering wheel spindle 11. The lower end of each spindle 1 1has a bifurcated end in the form of a yoke 12 fixed thereto and forrotation therewith. A ground wheel 14 is rotatable in the lower end ofeach yoke and an individual power plant in the form of an electric motor16 is supported within the yoke for driving its wheel through a chainconnection 17. In thismanner, each of the wheels is individually drivenby its own power plant. Each of the wheels is also rotatable on itsvertical spindle and therefore, each of the wheels is individuallysteerable. While the invention has been shown as applied to the cranefor steering of all four wheels, it will be understood that only twowheels at one end of the vehicle may be steerable.

As shown clearly in FIGS. 3 and 4, each of the steering spindles alsohas a sprocket 20 rigidly fixed therewith. A steering sprocket 22 isalso journalled adjacent each of the sprockets 20 by means of the stubshaft 23 which is fixed to the lower side of the sills 7 and 8. A rollerchain 25 is then trained around the steering sprocket 22 and around thespindle sprocket 20, and a tension adjusting sprocket 26 is alsoadjustably mounted on its shaft 27 on the sill for adjusting the tensionof the chain.

As the construction of each of the steering assemblies to be describedis the same for each of the wheels, only one will now be generallydescribed.

As shown clearly in FIG. 7, a pair of hydraulic power cylinders isprovided between each of the steering sprockets 22 and brackets 30 fixedto the lower side of the sills. More specifically, cylinders 32, 33 areprovided for one of the steering sprockets. Cylinders 34, 35 areprovided for the adjacent sprocket at the corresponding end of thecrane. The invention will be described in connection with the powercylinders 32 to 35 which are located at one end of the crane and areoperated together to effect turning movement at that end of the crane.

As previously stated however, the power cylinders and the steeringarrangement at the opposite end of the crane would be similar so thatall four wheels of this particular embodiment of the invention can besteered simultaneously. In this manner, a very short turning radius canbe obtained, in fact the gantry crane can be turned practically aboutits own vertical axis.

The connection of the power cylinders to their respective steeringsprockets 22 is in the form of a conventional ball stud 38 and acomplementary socket 39. The other end of the power cylinders areconnected to the brackets 30 of the frame by means of the pivotal block40.

The control cylinder 50 is shown in section in FIGS. 6 and 8, andincludes a cylinder barrel 60 to which the rod end head 61 is secured. Apiston rod 62 is slideable in the rear rod bushing 63 fixed in the head61. Suitable O-ring and wiper seals are provided as indicated. Aninternal spring retainer 64 is mounted in the 'annular chamber 65 formedbetween the barrel 60 and the rod 62 and a centering spring 66 actsagainst a spring retainer 67 abutting against an end flange 68, and alsoacts against the retainer 64 which abuts against the inner end of therod head 61.

A piston 70 is fixed to the piston rod 62 and sealingly slides within acylinder barrel 71 which is also fixed to the head 61. At the other endof the cylinder barrel 71 is fixed a head 73 which contains a fluidpassage 74 through which fluid can be introduced to and expelled fromannular chamber 75 located at one side of the piston 70. Another fluidpassage 76 is provided in head 61 and functions to convey fluid to andexpel fluid from the opposite working chamber 77 located at the otherside of the piston 70.

Admission of fluid through passage 76 into chamber 77 causes extensionof the piston rod 62. When fluid pressure isadmitted through passage 74,the piston 70 and its'attached rod 62 are urged into the contractingdirection. The retaining ring 79 fixed on the piston rod 62 picks up theinternal retainer 64 as the control cylinder is being contracted therebycompressing the spring 66. Spring 66 thus acts to return the piston 70to center after pressure has been relieved from the chamber 75. Thus,the control cylinder 50 is spring One of the power cylinders of each ofthe sprockets centered by means of the spring 66.

Thus extension and contraction of the control cylinder provides atwo-way, power operated control which barrel is rigidly fixed-at itsother end by its plate 93 to the plate 68 of the cylinder barrel 60. Aspring retainer 94 is slideable within barrel 91 and spring acts betweenretainer 94 and end plate 92, thus continually urging the retainer 94towards the piston rod 62. The inner end 62a of the piston rod 62 isadapted to abut against the retainer 94, when the control cylinder iscontracted beyond a predetermined point. Further contraction of thecontrol cylinder beyond this predetermined point acts to cause thepiston rod to compress the spring 90, thereby impeding and retardingcontinued contraction of the rod. Consequently, the reduced amount ofmovement of the piston 62 in the contracting direction results in lessfluid pressure being admitted through valve V to its attached powercylinder 33.

As shown in FIG. 7, when the operator desires to turn the vehicle to theleft, the wheel on the left side should be turned to a greater anglethan the wheel at the outer side of the turn. This differential turningof the wheels insures that no scuffing or skidding of the tires occursas the turn is being made. Thus when making a turn as indicated in FIG.7, the control cylinder 50 is being extended while the control cylinder51 at the inside of the turn is being contracted. Consequently,

due to the resistance offered by spring 90 in the control cylinder 51,the piston rod 62 and its adapter 80 move valve V a lesser distance tothereby admit a lesser amount of fluid to the power cylinder 34. On theother hand, extension of the control cylinder 50 is not influenced byits spring 90 and therefore when cylinder 50 is extended, the valve V ofpower cylinder 33 is operated normally and a normal amount of pressurefluid is admitted to the power cylinder 33 to enable it to extend in itsnormal manner. Consequently, the wheel of the gantry at the inside ofthe turn is operated through a greater angular movement than the wheelat the outer side of the turn.

In this manner, the oppositely acting control cylinders 50 and 51 supplydifferent quantities of pressure fluid to their respective powercylinders 33 and 34, respectively, thereby producing angular rotation oftheir steerable wheels in like direction, but in different magnitudes.No complicated linkages nor mechanical tie bars or drag links arenecessary to produce this dif ferential turning of the steerable wheels.

A more detailed reference will now be made to the power cylinder 33 andits valve V as well as to the fluid power circuit shown in FIGS. 7 and8.

The valve V includes a valve spool 100 which is connected to the controlrod 81 of the valve. A spring 101 acts to urge the valve spool 100 tothe neutral position. When the valve spool is shifted to the left asviewed in FIG. 8, fluid pressure enters the fluid inlet port 102 fromthe pump 103 and conduit 104. This fluid is then directed via passage111 in the valve body and to the rod end chamber of the power cylinder33. This causes contraction of the power cylinder 33. Fluid is alsodirected via flexible conduits 1 to the head end of the other powercylinder 32 extending the power cylinder. The fluid is expelled from rodend of cylinder 32 via passage 108 in side wall of the power cylinder 32through flexible conduit 107, through passage 112 in the valve and thenthrough conduit 113 to sump.

Shifting of the valve spool 100 in the opposite direction by the controlcylinder 50 (that is to the right as viewed in FIG. 7) acts in theopposite manner, that is to say, pressure fluid then flows from the pump103, through the inlet 102 and is directed to the passage 105 topressurize the head end of cylinder 33. This pressure fluid also flowsvia conduit 107 to the rod end of the other power cylinder 32, therebycontracting the latter while the power cylinder 33 extends.

The arrangement for the other wheel assembly is similar andcorresponding parts have been labeled with the same reference numeraland also the suffix letter a. Thus each wheel assembly has its separatefluid pumps which furnish pressure fluid to the power cylinders.

As shown in FIG. 7, a common fluid pressure pump 130 furnishes pressurefluid to a control valve CV. When the lever 131 of the control valve CVis swung as indicated, the plunger 132 of the control valve acts topermit pressure fluid to flow from the pump 130 to line 133 and to theport 76 of control cylinder 50 and port 74a of control cylinder 51.Under those conditions, fluid pressure is exhausted from the oppositeends of control cylinder 50 via line 135 and from the opposite end ofcontrol cylinder 51 via line 137. The control valve CV itself is dumpedto the sump via line 139.

The control valve itself is of the type shown in my copending US.application, Ser.,No. 874,443, filed Nov. 6, 1969, now US. Pat. No.3,605,8 l4 and entitled Improved Pressure Regulating Valve and if a moredetailed description of that valve is deemed to be either necessary ordesirable, reference may be had to said application.

With the vehicle as described, a separate power steering pump isprovided for each wheel, and consequently each wheel is powered steeredby fluid independently of the other wheel.

Control cylinders move only the servo-valves, and the actual force toturn the wheels is accomplished by the power cylinders.

In connection with the control cylinders, they are spring loaded to theneutral position, and consequently as control cylinders return toneutral, the control valve is returned to neutral. In other words, thecentering springs return the control cylinders to the neutral position,thereby turning the crane ground wheels back to a straight aheadposition, thereby providing automatic return of the ground wheels to thestraight ahead position, and this is accomplished hydraulically, and notas in other types of vehicles by the arrangement of the inclination ofthe kingpin pivot point mechanism.

The spring centered control cylinders, are modulated by additionalsprings to keep the power steered ground wheels in proper relationeither in a straight ahead position or to full turn in either directionwhen the same fluid pressure is applied simultaneously to each controlcylinder by the operator.

Iclaim:

1. In a vehicle of the type having a frame and at least a pair of spacedapart steerable wheel assemblies and each assembly including a yokepivotally mounted in said frame and a ground wheel rotatably mounted ineach of said yokes, apparatus for angularly rotating each of said yokesto effect steering of said vehicle, each of said apparatus comprising, adouble acting fluid power cylinder mounted on said frame and having aconnection with its respective yoke for rotating the latter in eitherdirection and to an extent determined by the amount of extension andcontraction of said power cylinders, each of said power cylinders havingservovalve means for determining the amount of fluid admitted to itspower cylinder and the direction of fluid through said cylinders, and anextensible control cylinder connected with each of said servo-valvemeans for actuation thereof, said control cylinders having resilientmeans for retarding movement of its control cylinder in one direction tothereby vary the amount of contraction of said control cylinder inrespect to its extension, whereby said control cylinders are operated inopposite directions and consequently said servo-valve means are actuatedin different amounts to cause said power cylinders to simultaneouslyproduce angular rotation of said yokes in like direction but todifferent degrees.

2. The vehicle set forth in claim 1 further characterized in that saidcontrol cylinder is attached at one end to said frame and is connectedat its other end to said servo-valve means.

3. The vehicle set forth in claim 1 including a separate fluid pressurepump for each of said apparatus.

5. The vehicle set forth in claim 4 further charac terized in that saidcontrol cylinder is attached at one end to said frame and is connectedat its other end to said servo-valve means.

6. The vehicle set forth in claim 1 further characterized in that saidcontrol cylinders also have resilient centering means for returning saidcontrol cylinders to a neutral position.

7. The vehicle set forth in claim 6 further characterized in that saidconnection between each of said power cylinders and its yoke comprises,a sprocket fixed to said yoke, a steering sprocket mounted on said frameand having an endless chain connected with said sprocket on said yoke,and said power cylinder is connected at one end to said steeringsprocket.

8. The vehicle set forth in claim 7 further characterized in that saidcontrol cylinder is attached at one end to said frame and is connectedat its other end to said servo-valve means.

1. In a vehicle of the type having a frame and at least a pair of spaced apart steerable wheel assemblies and each assembly including a yoke pivotally mounted in said frame and a ground wheel rotatably mounted in each of said yokes, apparatus for angularly rotating each of said yokes to effect steering of said vehicle, each of said apparatus comprising, a double acting fluid power cylinder mounted on said frame and having a connection with its respective yoke for rotating the latter in either direction and to an extent determined by the amount of extension and contraction of said power cylinders, each of said power cylinders having servo-valve means for determining the amount of fluid admitteD to its power cylinder and the direction of fluid through said cylinders, and an extensible control cylinder connected with each of said servo-valve means for actuation thereof, said control cylinders having resilient means for retarding movement of its control cylinder in one direction to thereby vary the amount of contraction of said control cylinder in respect to its extension, whereby said control cylinders are operated in opposite directions and consequently said servo-valve means are actuated in different amounts to cause said power cylinders to simultaneously produce angular rotation of said yokes in like direction but to different degrees.
 2. The vehicle set forth in claim 1 further characterized in that said control cylinder is attached at one end to said frame and is connected at its other end to said servo-valve means.
 3. The vehicle set forth in claim 1 including a separate fluid pressure pump for each of said apparatus.
 4. The vehicle set forth in claim 1 further characterized in that said connection between each of said power cylinders and its yoke comprises, a sprocket fixed to said yoke, a steering sprocket mounted on said frame and having an endless chain connected with said sprocket on said yoke, and said power cylinder is connected at one end to said steering sprocket.
 5. The vehicle set forth in claim 4 further characterized in that said control cylinder is attached at one end to said frame and is connected at its other end to said servo-valve means.
 6. The vehicle set forth in claim 1 further characterized in that said control cylinders also have resilient centering means for returning said control cylinders to a neutral position.
 7. The vehicle set forth in claim 6 further characterized in that said connection between each of said power cylinders and its yoke comprises, a sprocket fixed to said yoke, a steering sprocket mounted on said frame and having an endless chain connected with said sprocket on said yoke, and said power cylinder is connected at one end to said steering sprocket.
 8. The vehicle set forth in claim 7 further characterized in that said control cylinder is attached at one end to said frame and is connected at its other end to said servo-valve means. 